1. Field of the Invention
The present invention relates to a method for formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask, in particular, to a method for formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask by means of photolithographic technology for forming a microscopic pattern in a semiconductor device.
2. Description of the Background Art
In recent years semiconductor integration circuits have been achieved remarkably high levels of integration and miniaturization. Accompanying that, miniaturization of circuit patterns formed on a semiconductor substrate (hereinafter referred to simply as a wafer) has made rapid advances.
Above all, photolithographic technology is widely perceived as the basic technology in pattern formation. Accordingly, up until the present day a variety of developments and improvements have been achieved. However, the miniaturization of patterning shows no signs of abating and the requirements for the increase of resolution of patterns have become more stringent.
This photolithographic technology is a technology wherein a pattern of a photo mask (original layout) is copied onto the photoresist applied to a wafer so that the copied photoresist is used to pattern the lower layer film to be etched.
At the time of copying of this photoresist, development processing is applied to the photoresist and the type where the part of the photoresist to which light hits is removed through this development processing is called a positive type photoresist while the type where the part of the photoresist to which light does not hit is eliminated is called a negative type photoresist.
In general, a resolution limit R (nm) in photolithographic technology using a scaling down exposure method is represented as:
R=k1xc2x7xcex/(NA)
Here, the wavelength (nm) of the utilized light is denoted as xcex, numerical aperture of a projection optical system of the lens is denoted as NA and a constant depending on the resist process is denoted as k1.
As is known from the above equation, in order to increase the resolution limit R, that is to say, in order to gain an even smaller pattern a method for making the values of k1 and xcex smaller while making the value of NA larger should be considered. That is to say, the constant depending on the resist process should be made smaller while proceeding to make the wavelength shorter and to make NA higher.
However, improvement of the light source or lenses are technically difficult and a problem arises, on the contrary, in proceeding to make the wavelength shorter and the NA higher so that the focal point depth xcex4 (xcex4=k2xc2x7xcex/(NA)2) of light becomes shallower so as to induce the lowering of the resolution.
Under such circumstances, in manufacturing semiconductor integrated circuits it is necessary to form a microscopic pattern with a large process margin. A modified illumination method works effectively for formation of a concentrated pattern and is widely practiced. On the other hand, as for a method for formation of an isolated line pattern with a large process margin, there is the method of using a Levenson type phase shift mask.
However, in the case of the Levenson type phase shift mask, it is necessary to manufacture a phase shifter for converting the phase of the exposure light by 180xc2x0 and there is the problem that the mask is difficult to manufacture. In addition, since the Levenson type phase shift mask attempts to increase the resolution by positively interfering with the transmission light of different phases, there is the problem that lens aberration of the projection exposure apparatus influences the resolution so that the excellent characteristics which are supposed to be gained in the case of no aberration cannot be gained. Therefore, the method of using the Levenson type phase shift mask is in the condition where the practical use thereof hasn""t made progress.
In addition, a method for improving the process margin (so-called auxiliary pattern method) by arranging the lines of a line width which is not resolved on the mask along the originally patterned lines has been taken into consideration. However, in this method the dimension of the mask pattern becomes extremely small and there is a problem that inspection for defects of the mask is difficult.
The purpose of the present invention is to provide a method for the formation of a semiconductor device pattern, a method for designing a photo mask pattern, a photo mask and a process for a photo mask wherein it is possible to form a microscopic pattern without using an auxiliary pattern method, a phase shift mask or the like and wherein the defect inspection of a mask is easy.
A method for a semiconductor device pattern formation according to the present invention includes a first exposure step of exposing a first photoresist on a wafer surface by a projection exposure method through a first photo mask which has an aperture pattern for light transmission including a pair of lines with substantially same width which run parallel to each other with a gap and which are isolated from other aperture patterns for light transmission, and an exposure amount, defined by an energy given to the pattern which has a sufficiently large mask aperture when the first photoresist is exposed, is four or more times and twenty or less times as large as the exposure amount on the border where the first photoresist is converted from soluble to insoluble in a developer through exposure or the exposure amount on the border where the first photoresist is converted from insoluble to soluble in a developer through exposure.
According to a method for the formation of a semiconductor device pattern, the first photoresist is exposed through a so-called overexposure wherein the exposure amount is larger than an ordinary exposure via the first photo mask which has a pair of aperture patterns for light transmission. Thereby, a microscopic pattern can be formed wherein the fluctuation of the pattern dimension is small even when the focus is changed to a certain degree. In addition, the depth of focus (DOF), which is a focal range wherein a certain focusing performance can be maintained at a constant level, can be made large. Therefore, a microscopic pattern can be formed with a large process margin and with a high precision without using an auxiliary pattern method of a phase shift mask.
The above described method for a semiconductor device pattern formation preferably further includes a second exposure step wherein regions of the first photoresist corresponding to regions other than pairs of aperture patterns for light transmission are exposed after the first exposure step and before the development step of the first photoresist.
A complicated pattern can be dealt with by carrying out a double exposure in the above manner.
In the above described method for a semiconductor device pattern formation, the first exposure is preferably carried out by modified illumination.
Thereby, the resolution and the depth of focus can be further increased.
In the above described method for a semiconductor device pattern formation, the modified illumination is preferably carried out by using a ring band illumination stop in the illumination optical system.
Thereby, the resolution and the depth of focus can be increased.
In the above described method for a semiconductor device pattern formation, the modified illumination is preferably carried out by using a quadruple polar illumination stop in the illumination optical system.
Thereby, the resolution and the depth of focus can be increased.
In the above described method for a semiconductor device pattern formation, the first photo mask is preferably an attenuating phase shift mask including a semi-transmissive shielding film having the pair of aperture pattern, for light transmission. The semi-transmissive shielding film includes a material which shifts the phase of exposure light after transmitting the semi-transmissive shielding film so as to be a phase which is different by 180 degrees from the phase of exposure light after transmitting the pair of aperture patterns for light transmission and which makes the intensity of exposure light after transmitting the semi-transmissive shielding film smaller than the intensity of exposure light after transmitting the pair of aperture patterns for light transmission.
Processing limit can be further enhanced by using an attenuating phase shift mask in the above manner.
In the above described method for a semiconductor device pattern formation, a transmittance of exposure light of the semi-transmissive shielding film is preferably 2% or more and 10% or less.
Thereby, the effect of the phase shift mask can be exercised efficiently.
In addition, in the case that the transmission light of the exposure light of the semi-transmissive shielding film is less than 2% the intensity of the exposure light which has transmitted the semi-transmissive shielding film becomes too small so that the effect of the attenuating phase shift mask can""t be efficiently gained. In addition, in the case that the transmission of the exposure light of the semi-transmissive shielding film exceeds 10% the film thickness of the photoresist after the development by exposure light which has transmitted the semi-transmissive shielding film becomes 0 or is reduced so that the photoresist can""t be used an etching mask.
In the above described method for a semiconductor device pattern formation, in an exposure using a ring band illumination stop, a ratio (a/R) of a sine a of a maximum incident angle to the first photo mask of illumination light formed by an illumination optical system to a sine R of a maximum incident light beam angle in an image on a wafer by a projection optical system multiplied by a scaling down magnification r of the projection optical system (rxc3x97a/R) is preferably 0.6 or more and 0.9 or less.
Thereby, an excellent resolution can be gained.
In the above described method for a semiconductor device pattern formation, in an exposure using a ring band illumination stop, a sine b of a minimum incident angle to the first photo mask of illumination light formed by an illumination optical system is preferably xc2xd or more of the sine a of the maximum incident angle.
Thereby, an excellent resolution can be gained.
In the above described method for a semiconductor device pattern formation, in an exposure using a quadruple polar illumination stop, a ratio (a/R) of a sine a of a maximum incident angle to the first photo mask of illumination light formed by an illumination optical system to a sine R of a maximum incident light beam angle in an image on a wafer by a projection optical system multiplied by a scaling down magnification r of the projection optical system (rxc3x97a/R) is preferably 0.6 or more and 0.9 or less.
Thereby, an excellent resolution can be gained.
In the above described method for a semiconductor device pattern formation, in an exposure using a quadruple polar illumination stop, a ratio (b/R) of a sine b of a minimum incident angle to the first photo mask of illumination light formed by an illumination optical system to a sine R of a maximum incident light beam angle in an image on a wafer by a projection optical system multiplied by a scaling down magnification r of the projection optical system (rxc3x97b/R) is preferably 0.3 or more.
Thereby, an excellent resolution can be gained.
In the above described method for a semiconductor device pattern formation, a line width W1 of each of the pair of aperture patterns for light transmission preferably satisfies the relationship of 0.35 less than W1/(xcex/NA) less than 0.65 when a wavelength of exposure light is denoted as xcex and numerical aperture of the projection optical system is denoted as NA.
In an aperture pattern for light transmission with such a line width, a microscopic pattern can be formed with a large process margin and with a high precision.
In the above described method for a semiconductor device pattern formation, a gap W2 of the pair of aperture patterns for light transmission preferably satisfies the relationship of 0.35 less than W2/(xcex/NA) when a wavelength of exposure light is denoted as xcex and numerical aperture of the projection optical system is denoted as NA.
In an aperture pattern for light transmission with such a line width, a microscopic pattern can be formed with a large process margin and with a high precision.
In the above described method for a semiconductor device pattern formation, a gap W3 between the pair of aperture patterns for light transmission and the other aperture patterns for light transmission preferably satisfies the relationship of 0.70 less than W3/(xcex/NA).
By maintaining the gap W3 with other aperture patterns for light transmission in this manner, a microscopic pattern can be formed with a large process margin and with a high precision.
In the above described method for a semiconductor device pattern formation, a length L of each of said pair of aperture patterns for light transmission preferably satisfies the relationship of 1.3 less than L/(xcex/NA).
In the aperture patterns for light transmission of such a length L, a microscopic pattern can be formed with a large process margin and with a high precision.
The above described method for a semiconductor device pattern formation includes: the step of patterning by developing the exposed first photoresist; the step of processing a first film to be processed under the first photoresist using the patterned first photoresist as a mask; the step of applying a second photoresist after the first photoresist is removed; the step of a second exposure for exposing a region of the second photoresist which correspond other regions except regions sandwiched between the pair of lines of the aperture pattern for light transmission; the step of patterning by developing the exposed second photoresist; and the step of processing the first film to be processed under the second photoresist using the patterned second photoresist as a mask.
Thereby, a complicated microscopic pattern can be copied to the film to be processed with a high precision.
The above described method for a semiconductor device pattern formation preferably further includes the step of patterning a second film to be processed below the first film to be processed using, as a mask, the first film to be processed which has been processed by using, as a photo mask, the first and the second layers of photoresist.
Thereby, by using the film to be processed as a hard mask the layer below it can be patterned.
In the above described method for the formation of a semiconductor device pattern, the material of the first film to be processed includes a silicon oxidation film and the material of the second film to be processed includes a polycrystal silicon.
The materials of the first and the second films to be processed can be selected in this manner.
In the above described method for the formation of a semiconductor device pattern, the first exposure is, preferably, carried out a plurality of times before the first photoresist is developed.
Thereby, a complicated pattern can be dealt with.
In the above described method for the formation of a semiconductor device pattern, the second exposure is, preferably, carried out a plurality of times before the second photoresist is developed.
Thereby, a complicated pattern can be dealt with.
A method for designing a photo mask pattern according to the present invention includes the following steps.
First, figure parts of microscopic line pattern is extracted from a design pattern layout. And the line width W2 of the mask dark lines in the figure parts of microscopic line pattern is adjusted so as to satisfy the relationship of 0.35 less than W2/(xcex/NA), wherein the wave length of exposure light is denoted as xcex and the numerical aperture of the projection exposure system is denoted as NA. Then a pair of aperture patterns for light transmission which have the line width of W1 satisfying the relationship of 0.35 less than W1/(xcex/NA) less than 0.65 are arranged so as to sandwich the mask dark lines of the line width W2.
Thereby, it becomes possible to design a photo mask pattern which can form a microscopic pattern with a large process margin and with a high precision.
In accordance with a process for a photo mask according to the present invention, a photo mask having, at least as a part of the entire pattern, the pair of aperture patterns for light transmission based on the line widths W1 and W2, calculated out by the above described method for designing a photo mask pattern, is produced.
Thereby, a photo mask which has the above described mask pattern can be processed.
A photo mask according to the present invention comprises a substrate and a shielding film. The substrate has a main surface. The shielding film is formed on the main surface of the substrate and has a pair of aperture patterns for light transmission with substantially the same line width which run parallel to each other for the gap and are isolated from other aperture patterns for light transmission. When the line width of the pair of aperture patterns for light transmission is denoted as W1, the gap between the pair of aperture patterns for light transmission is denoted as W2, and the minimum gap between the pair of the aperture patterns for light transmission and other aperture patterns for light transmission is denoted as W3, each of W1, W2 and W3 satisfies the relationships of 0.54 less than W2/W1 and 1.08 less than W3/W1.
Thereby, a photo mask which can form a microscopic pattern with a large process margin and a high precision can be gained.